The story behind the stupa is that when Buddha passed away, his remains were cremated and the ashes divided and buried under eight dirt mounds - each mound commemorating one of the eight great deeds that he was said to have accomplished during his life. Two two additional stupas were constructed to encase the funerary urn and the embers.
According to Bhuddist teaching, every element of Bhudda's physical body is imbued with enlightenment. Thus, even after cremation, the remains are considered sacred because they are the distilled essence of his physical form and therefore, themeselves are the embodiment of enlightenment. Because it enshrines remains of Buddha, the stupa has evolved over time from being a funerary monument to being an object of religious veneration. It is the chief symbolic representation of Bhuddism as the cross symbolizes Christianity.
As Buddhism spread throughout Asia, the stupa took on variations in local styles and designs. However, common elements remain.
Overall, the shape of the stupa is intended to represent the Buddha, crowned and sitting in meditation posture on a lion throne.
The basic sections of the stupa are:
A hemispherical dome that houses sacred objects.
A tiered platform that that is often referred to as the "throne"and which is said to represent the five elements of existence - earth, water, fire, air, space.
A 13 ring conical spire, the design of which is supposedly derived from the ceremonial umbrellas which used to be present on top of the earliest Indian structures. The thirteen rings are said to symbolize the thirteen stages of a would-be Buddha's advance towards Buddhahood.
....and topping the spire, the "drop", a circular disc atop a lunar crescent symbolizing the sun resting on the moon. The drop is said to represent a jewel which is symbolic of enlightenment, the sun representing wisdom and the moon representing compassion or 'heart of awakening'.
The stupa also symbolizes the five elements and colors and their relationship to the Enlightened Mind:
- Base – Square – Yellow – Earth - Equanimity
- Dome – Circle – White – Water - Indestructibility
- Spire – Triangle – Red – Fire – Compassion
- Parasol – Half Circle – Green – Wind – All- accomplishing Action
- Jewel – Dewdrop (no shape/no color/void) – Space – All-pervading Awareness
There's a lot of complex symbolism to the stupa and I don't know that I will ever understand it all but I do appreciate its signficance to the followers of Bhudda.